As portable small electric/electronic devices are widely propagated, new secondary batteries such as a nickel metal hydride battery and a lithium secondary battery are actively being developed.
The lithium secondary battery uses metal lithium as an anode active material and a non-aqueous solvent as an electrolyte. Lithium can generate a high voltage because it has considerable ionization tendency, and thus a battery having a high energy density using lithium is under development. The lithium secondary battery using metal lithium as an anode active material has been used as a next-generation battery for a long time.
However, the lithium secondary battery has a short life cycle because lithium dendrites grow from the anode and penetrate an insulating membrane as charging and discharging of the lithium secondary battery are repeated, resulting in short-circuit with the cathode, causing battery failure.
To solve the problem that the life cycle of the lithium secondary battery is reduced due to anode deterioration, a method of using a carbon-based material capable of intercalating/deintercalating lithium ions instead of metal lithium as an anode active material was proposed.
In a lithium secondary battery having an anode formed using a carbon-based material, the lithium ions are intercalated into carbon according to reaction at the cathode during charging/discharging. Electrons are transferred to a carbonaceous material of the anode and thus carbon is negatively charged to deintercalate the lithium ions from the cathode and intercalate the lithium ions into the carbonaceous material of the anode during charging, whereas the lithium ions are deintercalated from the carbonaceous material of the anode and intercalated into the cathode during discharging. Using this mechanism, precipitation of metal lithium at the anode can be prevented to achieve a lithium secondary battery having a considerably long life cycle.
The lithium secondary battery using a carbon-based material as an anode active material is called a lithium ion secondary battery and has been widely propagated as a battery of portable electronic/communication devices. However, when a carbon-based material is used as an anode active material, the charge/discharge potential of lithium is lower than the stable range of a conventional non-aqueous electrolyte, and thus decomposition of electrolyte occurs during charging/discharging, causing low initial charging/discharging (coulombic) efficiency of the current lithium secondary battery using a carbon-based material as an anode material, short battery lifespan, and deterioration of high rate capability. Accordingly, methods for stabilizing the surface of a carbon-based anode active material using an electrolyte additive having a decomposition potential higher than that of a carbonate-based electrolyte, such as VC (vinylene carbonate), FEC (fluoroethylene carbonate), etc. are proposed in order to increase the lifespan of a non-aqueous lithium secondary battery using a carbon-based material.
However, the electrolyte additive cannot solve the problems of high rate capability and charging/discharging efficiency deterioration although it increases the lifespan of the lithium secondary battery.